getbits.c

xmms-1.2.10.tar.gz学习使用的就下吧

#include "mpg123.h"

#if 0
static void check_buffer_range(int size)
{
	int pos = (bsi.wordpointer-bsbuf) + (size >> 3);

	if( pos >= fsizeold) {
		fprintf(stderr, "Pointer out of range (%d,%d)!\n", pos, fsizeold);
	}
}
#endif

void mpg123_backbits(int number_of_bits)
{
	bsi.bitindex    -= number_of_bits;
	bsi.wordpointer += (bsi.bitindex>>3);
	bsi.bitindex    &= 0x7;
}

int mpg123_getbitoffset(void) 
{
	return (-bsi.bitindex)&0x7;
}

int mpg123_getbyte(void)
{
#ifdef DEBUG_GETBITS
	if(bsi.bitindex) 
		fprintf(stderr,"getbyte called unsynched!\n");
#endif
	return *bsi.wordpointer++;
}

unsigned int mpg123_getbits(int number_of_bits)
{
	unsigned long rval;

#ifdef DEBUG_GETBITS
	fprintf(stderr, "g%d", number_of_bits);
#endif

	if(!number_of_bits)
		return 0;

#if 0
	check_buffer_range(number_of_bits + bsi.bitindex);
#endif

	{
		rval = bsi.wordpointer[0];
		rval <<= 8;
		rval |= bsi.wordpointer[1];
		rval <<= 8;
		rval |= bsi.wordpointer[2];

		rval <<= bsi.bitindex;
		rval &= 0xffffff;
		
		bsi.bitindex += number_of_bits;

		rval >>= (24-number_of_bits);

		bsi.wordpointer += (bsi.bitindex >> 3);
		bsi.bitindex &= 7;
	}

#ifdef DEBUG_GETBITS
	fprintf(stderr,":%x ",rval);
#endif

	return rval;
}

unsigned int mpg123_getbits_fast(int number_of_bits)
{
	unsigned int rval;
#ifdef DEBUG_GETBITS
	fprintf(stderr,"g%d",number_of_bits);
#endif

#if 0
	check_buffer_range(number_of_bits+bsi.bitindex);
#endif

	rval =  (unsigned char) (bsi.wordpointer[0] << bsi.bitindex);
	rval |= ((unsigned int) bsi.wordpointer[1] << bsi.bitindex) >> 8;
	rval <<= number_of_bits;
	rval >>= 8;

	bsi.bitindex += number_of_bits;

	bsi.wordpointer += (bsi.bitindex >> 3);
	bsi.bitindex &= 7;

#ifdef DEBUG_GETBITS
	fprintf(stderr,":%x ",rval);
#endif
	return rval;
}

unsigned int mpg123_get1bit(void)
{
	unsigned char rval;

#ifdef DEBUG_GETBITS
	fprintf(stderr,"g%d",1);
#endif

#if 0
	check_buffer_range(1+bsi.bitindex);
#endif

	rval = *bsi.wordpointer << bsi.bitindex;

	bsi.bitindex++;
	bsi.wordpointer += (bsi.bitindex >> 3);
	bsi.bitindex &= 7;

#ifdef DEBUG_GETBITS
	fprintf(stderr,":%d ",rval >> 7);
#endif

	return rval>>7;
}